Image Guided Intravascular Therapy Catheter Utilizing a Thin Chip Multiplexor

ABSTRACT

A medical device that includes an array of ultrasound elements and an integrated circuit, proximal to the ultrasound elements, having a thickness of less than 40 μm, and having an array of ultrasound element driving-and-receiving contacts, matching the array of ultrasound elements and collectively electrically connected to each of the ultrasound elements. The integrated circuit also having a set of input-output signal contacts, the set being collectively switchable into contact with any one of a set of predefined blocks of driving-and-receiving contacts, and a set of control contacts, wherein inputs received by the control contacts collectively command some aspect of chip operation. The medical device further includes a set a protective covering.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 15/633,716, filed Jun. 26, 2017, which is incorporated byreference as if fully set forth herein.

BACKGROUND

U.S. Pat. No. 8,702,609, which is assigned to the assignee of thepresent application, discloses an image guided-therapy catheter thatuses ultrasound to form an image of the interior of a blood vesseldirectly in front of the catheter, to determine the locations of plaque,and then permits the use of this information in driving a set of RFablation electrodes to selectively ablate plaque, while avoidingdamaging the interior surfaces of the blood vessel. A number ofchallenging issues are presented in the design of this type of device.Among these is the acoustic characteristics of the medical device andhow to avoid harmful interference to the returning signal from signalthat has reflected from the portion of the device proximal (that is,further back from the tip) to the ultrasound array.

Another troublesome issue in the design of the system is themultiplexing of the driving/receiving coax lines for the ultrasoundelements. With a large array, it would be impossible to have a separatecoax line for each element. Multiplexors, however, require an increasingnumber of control inputs for an increasing number of multiplexed lines.With catheter space at an extreme premium, fitting a high number ofcontrol lines into a catheter is also very problematic.

SUMMARY

The following embodiments and aspects thereof are described andillustrated in conjunction with systems, tools and methods which aremeant to be exemplary and illustrative, not limiting in scope. Invarious embodiments, one or more of the above-described problems havebeen reduced or eliminated, while other embodiments are directed toother improvements.

The present invention may take the form of an intravenous ultrasoundcatheter having a distal tip and having a forward-facing array ofultrasound elements near to the distal tip of the device. Also, anintegrated circuit (IC) die, abuts and is proximal to the ultrasoundelements, having a thickness of less than 80 μm, and further having afirst face, facing the forward-facing array, and having an array ofultrasound element driving and receiving contacts, in mating arrangementto the array of ultrasound elements, so that the array of ultrasoundelement driving and receiving contacts collectively physically abut andelectrically connect to each of the ultrasound elements; a second face,opposed to the first face, and having a set of input-output signalcontacts, the set being fewer in number than the array of ultrasoundelement driving and receiving contacts and each being switchable intocontact with any one of a set of the ultrasound element driving andreceiving contacts, the second face also having a set of controlcontacts, wherein inputs received by the control contacts positivelycollectively command some aspect of operation of the IC die; and a setof amplifiers, interposed between the first face and the second face,including an amplifier for each one of the driving and receivingelectrical contacts. A flex circuit assembly is proximal to theintegrated circuit and including coax cables and a contact portion, hasa set of contact pads abutting and electrically connects theinput-output signal contacts of the IC die to the coax cables. Finally,backing material, abutting and directly proximal to the contact portion,thereby forming an interface and wherein the backing material and thecontact portion material have equal acoustic impedance, therebypreventing reflection at the interface.

In addition to the exemplary aspects and embodiments described above,further aspects and embodiments will become apparent by reference to thedrawings and by study of the following detailed descriptions.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments are illustrated in referenced drawings. It isintended that the embodiments and figures disclosed herein are to beconsidered illustrative rather than restrictive.

FIG. 1 is a block diagram of the ultrasound system of a medical device,according to the present invention.

FIG. 2 is a physical representation of the proximal side of the mux andamp chip shown in block form in FIG. 1.

FIG. 3 is a proximal side view of the elements of the ultrasound array,shown in block form in FIG. 1, showing one allocation of ultrasoundelements into eighteen blocks 1 through H.

FIG. 4 is a side rear isometric view of the imaging head of the systemof FIG. 1.

FIG. 5 is a view of an article of flex circuit used in the system ofFIG. 1.

FIG. 6 is an illustration of the flip chip technique which may be usedas a step in the production of the imaging head of FIG. 5.

FIG. 7 is a side rear isometric view of the imaging head of FIG. 5,shown including further proximal elements.

FIG. 8 is a diagram of a catheter configured for placement through anopening and into the body of a human patient or subject.

FIG. 9 is a cross-sectional view of a catheter in a Seldinger sheath.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1 and 2, in a first preferred embodiment of anultrasound imaging system 10, having a distal portion housed in acatheter sized to enter cardiac arteries, a processor assembly 12commands a waveform signal generating network 14, which generates 35 MHzwaveforms for 32 coax signal lines 16, which drive and receive from aset of 32 input/output contacts 17, on an integrated circuit die(henceforth “multiplexor chip” or “chip”) 18. In one preferredembodiment, multiplexor chip 18 is less than 12 μm in thickness. Inalternative embodiments, chip 18 is less than 20, 40, 60 and 80 μm.Control lines 20A-20D extend from processor 12 to multiplexor 18,attaching to contact pads 21A-21D, respectively, and must commandmultiplexor 18, for each phase to switch the 32 signal lines 16 to a oneout of a set of 18 designated blocks 22 of drive/sense contacts, todrive one out of 18 blocks of thirty-two ultrasound elements in a 24×24(576) ultrasound element array 30. In a preferred embodiment array 30 ismade of a piezoelectric material, such as a piezoelectric ceramic. It ispossible that at some point another technology, such as capacitivemicromachined ultrasound transducers (CMUT) may be usable in thisapplication. Thirty-two micro-coax lines are required for theinput/output contacts 17 with the grounds tied together and theneventually to a common ground (analog ground 19) on the chip. Plus, fourmore wires are required for digital or logic control and power to the ICchip. In addition, in one embodiment four wires are required to transmitthe RF signals to RF ablation electrodes (noted below). These wiresphysically bypass chip 18.

The basic function of the chip is to allow 32 micro-coax acousticchannels to selectively connect to any group of thirty-two ultrasoundarray elements and to amplify the return signals from the ultrasoundelements, as they are transmitted to the coax signal lines 16. Onpower-up the ultrasound system resets the chip and asserts the Tx/Rxline placing the MUX in transmit mode for elements 1-32. The ultrasoundsystem then transmits an electrical analog pulse through each of themicro-coax cables to contacts 17. The electrical pulses are thentransferred to elements 1-32 of the piezoelectric array. After theultrasonic pulses have left elements 1-32, the Tx/Rx line is de-assertedplacing the MUX in receive mode. In the receive mode mechanical energyreflected from the tissue or blood is converted to electrical energy bythe piezoelectric elements 1-32 and the power transferred back throughthe chip where the signal is amplified (using power received on contactpad 23), matched to the cable and sent back through each micro-coax tothe ultrasound system for conversion to digital data at the front end ofthe imaging system. The Receive mode lasts for approximately 8 μS. Tx/Rxis then re-asserted and the cycle repeats for element 33-64 and soforth. A chip ground 25 is electrically connected to a further ground atthe proximal end of a linear conductor.

During the transmit cycle the input electrical impedance of the IC chipon the flex side of the chip is matched to that of the coaxial cable(typically 50 to 100 Ohm characteristic impedance), whereas the outputimpedance of the IC chip is matched, or optimized, to the electricalimpedance of the individual piezoelectric elements of the array(typically 10,000 Ohms). The electrical impedance matching scheme worksalso in the receive cycle to enable optimal transmission of power.

In summary the IC chip performs multiple functions in the operation ofthe imaging system: It enables the electrical connection of multiplemicro-coaxial cables to the individual elements of the array, it matchesthe electrical impedance of the coaxial cables to that of thepiezoelectric elements, it acts as multiplexer so the entire array ofelements can be addressed and as an amplifier of the weak receivesignals (of the order of a few microvolts) in receive mode.

In one scheme of driving the ultrasound array 30, the following transmitreceive sequence is performed, where B₁ is the first block of elements,B₂ is the second block of elements and so on until B₃₂ is the 32^(nd)block of elements and TB_(n) indicates transmission through the nthblock of elements, and RB_(n) means receiving on the nth block ofelements:

TB₁,RB₁,TB₁,RB₂, . . . ,TB₁,RB_(n),TB₂,RB₁,TB₂,RB₂, . . . TB₂,RB_(n), .. . ,TB_(n)RB₁, . . . TB_(n)RB_(n)  (S1)

In a catheter designed to be introduced into cardiac arteries, space isat a great premium, and any design aspects that reduce the number oflines that must extend through the catheter yield a great benefit.Although a traditional multiplex device would permit any block 32 to bechosen at any time, this would require 5 control lines (yielding 32combinations), not counting a transmit/receive choice line. Lowering thenumber of blocks to 16 would require blocks of 36—requiring four morecoax signal lines 16, also difficult to fit into the catheter. Toaccommodate the above pattern of transmit and receive sequences, in onepreferred embodiment control line 20 b is a transmit line increment. Inone preferred embodiment, chip 18 includes an incrementing register fortransmit periods, incremented by a transmit increment line 20 b and aseparate incrementing register for receive periods, incremented by areceive increment line 20 c. A transmit/receive selector line 20 athereby permits each to be incremented through its repeated cycles, asshown in sequence S1, listed above. In another embodiment,transmit/receive selector line 20 a is used to increment the transmitand receive block registers, with for example, each rising edge countingas a transmit block increment and each falling edge counting as receivedblock increments. A counter is placed in series with the transmitregister so that only every 18th transition to transmit increments thetransmit register and with every transition to receive incrementing thereceive register, as indicated in sequence S1. This permits the transmitand receive increment lines to be eliminated. In yet another preferredembodiment, a single block increment line steps through the 18×18 (324)transmit/receive pairs sequence S1, which must be stored in a memory 36of chip 18.

Chip 18 is connected to array 30, by way of different techniques such asa flip chip bonding technique, pressure bonding through a thin layer oflow viscosity adhesive (1-2 microns) or indium bonding. These are knowntechniques in the semiconductor/microchip industry. In the case of flipchip bonding, for example, a solder ball 40 is constructed on each chipcontact 42, and then these solder balls are pressed into array 30,slightly crushing solder balls 40, to form a good bond, and to createrobust electrical connections between each chip contact 42, and eachelement of array 30. In this process, the thinness of chip 18 is a greatadvantage, because even though solder balls 40 have some thickness, thecapability of chip 18 to bend slightly, due to its thinness, greatlyfacilitates the formation of a robust bond between solder balls 40 andeach element of array 30. Adhesive filler is added among the thin solderballs to increase strength as well as conduct acoustic energy into thedissipative backing. In the case of pressure bonding electricalconductivity is achieved through the surface roughness of the bondedsubstrates, the high points of which penetrate enough through the thinlayer of adhesive to assure electrical connection. In the case of indiumboding conductive pads on both substrates (silicon chip and flexcircuit) are metalized with a one to three thousand angstroms of indiumwhich then flows through the application of heat at a low temperature(about 170 C). In addition, chip 18 is approximately 10 μm thick thuseffectively becoming an “anti-matching” layer and an integral part ofthe acoustic architecture as opposed to a thicker chip. Computersimulations indicate that the thickness of the silicon chip can befurther tweaked to achieve improved pulse properties.

The waveforms created by waveform generator 14 are typically two-cycle35 MHz pulses, having pulse width of 5.7 nsec and pulse repetitionfrequency for 6 mm maximum penetration of 125 kHz or pulse repetitionperiod of 8 usec. It should be noted that other frequencies in the rangeof 25 to 50 MHz may be utilized depending on resolution or penetrationdesired.

Referring, now, to FIGS. 4, 5, 6 and 7, in one preferred embodiment,multiplex chip 18 forms a portion of an imaging and ablation head 41 asdescribed in detail in U.S. Pat. No. 8,702,609. The proximal side ofmultiplex chip 18 is attached to a central portion 43 (which may also bereferred to as the “contact portion”) of a flex circuit 44, having fourarms 46, that are bent proximally and that each include a number of thesignal coax cables 16, and for which at least one includes one or morecontrol lines, such as lines 20A-D. Ultrasound absorbent backingmaterial 48 is proximal to central portion 42. This material is apolymer or polymer blend chosen for its ability to absorb high frequencyultrasound and in particular, ultrasound in the range of 20-50 MHz. Thelossy backing material has the same acoustic impedance as the flexcircuit material, including the material of contact portion 43, to avoidreflection at the interface between the two. Proximal to backingmaterial 48 is a radiopaque marker 50. After extending proximally pastmarker 50, flex circuit arms 46 are connected to a group of coax cablesand other conductors, for signals to travel to a base station (notshown).

Referring to FIG. 8, in a preferred embodiment, ultrasound system 10 isphysically implemented in a vascular imaging and plaque ablationcatheter system 60. System 60 is arranged to provide images internal tobody B for medical diagnosis and/or medical treatment. System 60includes a control station comprising an ultrasound imaging system 62,of which processor assembly 12 and waveform generator and receiveamplifier 14 form a portion, and an RF therapy system 70, each of whichare operatively coupled to catheter 80, as well as appropriate operatorinput devices (e.g. keyboard and mouse or other pointing device of astandard variety) and operator display device (e.g. CRT, LCD, plasmascreen, or OLED monitor).

Catheter 80 is configured for placement through opening O and into bodyB of a human patient or subject, as schematically represented in FIG. 8.Catheter 80 is preferably configured for insertion into a blood vesselor similar lumen L of the patient by any conventional vascular insertiontechnique. Catheter 80 includes a guide wire lumen that extends from aproximal port 82 through the distal tip 84 of the catheter 80, which isused to insert catheter 80 over a pre-inserted guidewire (not shown) viaa conventional over the wire insertion technique. The guidewire exitport may be spaced proximally from the distal tip, accordingly, to knowndesign. Catheter 80 may be configured with a shortened guidewire lumenso as to employ a monorail type insertion technique, or catheter 80 maybe configured without any guidewire lumen and instead configured forinsertion through the lumen of a pre-inserted guide catheter.

Referring to FIG. 9, in one catheter embodiment 110, designed to beintroduced into a blood vessel by of a sheath 112, according to theSeldinger method of catheter placement, a larger area lumen 114 isavailable for placement of coax cables, because the space for aguidewire is no longer necessary. RF and digital control wires 116extend inside the side wall 118. In the Seldinger method a guidewire isused to facilitate the placement of the sheath 112. The guidewire isremoved, and the sheath 112 is then used to guide the catheter 110.Because the space for the guidewire is eliminated, the number of coaxcables may be increased, relative to an embodiment in which there is aspace for a guidewire. There is an indication that with the embodimentof FIG. 8, 64 coaxial cables could be fit into the catheter, indicatingthat a 576 element array could be driven in 9 transmit/receive cycles.

Referring now to FIG. 8, the mux and amp chip 18 and ultrasound elementsarray 30 are located in distal end 84, whereas a set of RF ablationelectrodes (not shown) form distal tip 86, which is designed to ablatearterial plaque P. Mini coax cables 16 extend through a side cable 88and then through a lumen in catheter 80, together with control signalwires 20A-20D (which in one embodiment extend through the flexibleexterior wall of catheter 80).

If the supporting tip surface is constructed of a suitable syntheticmaterial capable of withstanding the high temperatures generated by theelectrodes, the electrode material may be deposited or applied directlyonto the tip. Suitable synthetic materials include high temperatureplastics (e.g. Torlon, available from Solvay Advanced Polymers LLC,Alpharetta, Ga.) or silicone rubber materials (e.g. RTV325, EagerPlastics, Inc. Chicago, Ill. or RTV 560 GE Plastics). Another suitablematerial, TPX (4-polymethylpentene) is available from Mitsui ChemicalsInc., Tokyo, Japan. TPX is a solid plastic with acoustic propertiessimilar to human tissue and therefore transports acoustic energy totissue efficiently with little loss. The acoustic impedance of humantissue is about 1.55 MRayls while that of TPX is 1.78 MRayls (implying93% transmission). TPX also has a relatively high softening temperature(about 350 F) and melting temperature of about 460 F, which makes itsuitable for the ablation application, in which elevated temperaturesmay occur.

While a number of exemplary aspects and embodiments have been discussedabove, those possessed of skill in the art will recognize certainmodifications, permutations, additions and sub-combinations thereof. Itis therefore intended that the following appended claims and claimshereafter introduced are interpreted to include all such modifications,permutations, additions and sub-combinations as are within their truespirit and scope.

1. An intravenous ultrasound catheter having a distal tip andcomprising: (a) a forward-facing array of ultrasound elements near tosaid distal tip of said device; (b) an integrated circuit (IC) die,abutting and proximal to said ultrasound elements, having a thickness ofless than 80 μm, and having: (i) a first face, facing saidforward-facing array, and having an array of ultrasound element drivingand receiving contacts, in mating arrangement to said array ofultrasound elements, so that said array of ultrasound element drivingand receiving contacts collectively physically abut and electricallyconnect to each of said ultrasound elements; (ii) a second face, opposedto said first face, and having a set of input-output signal contacts,said set being fewer in number than said array of ultrasound elementdriving and receiving contacts and each being switchable into contactwith any one of a set of said ultrasound element driving and receivingcontacts, said second face also having a set of control contacts,wherein inputs received by said control contacts positively collectivelycommand some aspect of operation of said IC die; and (iii) a set ofamplifiers, interposed between said first face and said second face,including an amplifier for each one of said driving and receivingelectrical contacts; (iv) wherein impedance of said ultrasound elementdriving and receiving contacts is matched to impedance of saidultrasound elements; (c) a flex circuit assembly, proximal to saidintegrated circuit and including coax cables and a contact portion,having a set of contact pads abutting and electrically connecting saidinput-output signal contacts of said IC die, to said coax cables; and(d) backing material, abutting and directly proximal to said contactportion, thereby forming an interface and wherein said backing materialand said contact portion material have equal acoustic impedance, therebypreventing reflection at said interface.
 2. The intravenous ultrasoundcatheter of claim 1, wherein said flex circuit includes a centralportion, having contact pads for said input/output and control contactsof said IC die and also includes arms having signal lines for carryingsignals from and to said IC die.
 3. The intravenous ultrasound catheterof claim 1, wherein said ultrasound array includes more than 256elements and has dimensions of less than 2 mm by 2 mm.
 4. Theintravenous ultrasound catheter of claim 1, further including a set ofablation catheters, positioned forward of said array of ultrasoundelements so that said ultrasound elements transmit and receive throughsaid set of ablation catheters.
 5. The intravenous ultrasound catheterof claim 1, wherein said array of ultrasound elementdriving-and-receiving contacts is flip chip bonded to said array ofultrasound elements.
 6. The intravenous ultrasound catheter of claim 1,wherein said flex circuit further includes a coax cable for eachinput/output contact.
 7. The intravenous ultrasound catheter of claim 1,further including a waveform generator, generating a waveform having afrequency of between 20 MHz and 50 MHz, and wherein said thin chip has athickness of one-quarter of the waveform wavelength for the speed ofsound through said thin chip material.
 8. The intravenous ultrasoundcatheter of claim 1, further including RF ablation electrodes positioneddistal to said ultrasound elements.
 9. The intravenous ultrasoundcatheter of claim 1, wherein said IC die has a thickness of less than 20μm.
 10. The intravenous ultrasound catheter of claim 1, wherein said ICdie has a thickness of less than 12 μm.
 11. The intravenous ultrasoundcatheter of claim 1, wherein impedance of said input-output signalcontacts matches impedance of contacts pads of said flex circuit.